It is known that glasses whose surfaces are darkened may be used to prepare many different products. Thus, for example, a surface darkened glass in the form of a disc may have its faces polished so that they transmit light through the visible region of the spectrum but have its perimeter substantially absorb such light. The lens so formed will absorb stray light near its perimeter but transmit such light near its center.
The surface darkened glass described above has conventionally been made by a process in which a clear glass core is enveloped with a dark glass cladding and both are subjected to heat and applied pressure to fuse them into a single unit. This process often produces glass objects with imperfections at the interface of the core and the cladding; and, when the surface of such a glass object is polished, pitting and other imperfections often appear at such interface.
It is an object of this invention to provide a process for preparing an integral surface darkened glass object which consists essentially of one glass which has substantially fewer imperfections than the prior art glass article, which consists of two separate glasses bonded together to form a single unit.